Friday, July 6, 2007

What do AIDS and cervical cancer have in common? Both are caused by viruses, transmitted sexually and disproportionately affect poor women and women of color. But AIDS still cannot be prevented by a vaccine while cervical cancer can.

The product behind the call is a vaccine against human papilloma virus (HPV), the major cause of cervical cancer. Still unclear to me is how much the vaccine formulation that's being marketed in the richer parts of the world will have to be retooled for other countries.

After all, there are a number of different subtypes of HPV that cause cancer--HPV-16 and HPV-18 being the most common culprits in the U.S. But other subtypes, like HPV-35, may be more troublesome in other parts of the world, as I wrote last May in A Geographical Puzzle on HPV.

Can there be a truly global vaccine against cervical cancer? What sort of testing, reformulation will be required? Will the incentive to do so disappear if the same vaccine that has already been developed for women in the richest part of the world can't be used everywhere?

3 comments:

Vivien Tsu
said...

This raises an important issue that is often a problem with some vaccines and even medicines. Fortunately, in the case of cervical cancer the picture is pretty uniform around the world. Although the distribution of HPV types in the general population does vary by region, the types that cause the most cancer do not. A new meta-analysis has just been published online that gathered all the studies of cervical cancer patients (14,595) and women with pre-cancer (7,094) where the HPV type had been identified. Here are the key results from the abstract of that review:

“In ICC [invasive cervical cancer], HPV16 was the most common, and HPV18 the second most common, type in all continents. Combined HPV16/18 prevalence among ICC cases was slightly higher in Europe, North America and Australia (74-77%) than in Africa, Asia and South/Central America (65-70%). The next most common HPV types were the same in each continent…”

At a minimum, 65% of the cervical cancer in every part of the world is due to the two types (16 and 18) in the current vaccines. Women in poor countries won’t need to wait years for a new vaccine that works for them; the current vaccines will do the job. We can get started now in preventing this scourge in the countries where it does the most harm—the developing countries that have not had access to the screening services that brought down the rates of cervical cancer in the industrial world decades ago. (The article is by Smith JS, Lindsay L, Hoots B, Keys J, Franceschi S, Winer R, Clifford GM. Human papillomavirus type distribution in invasive cervical cancer and high-grade cervical lesions: A meta-analysis update. Int. J. Cancer. 2007 Aug 1;121(3):621-32.)

Your questions are big ones, Christine--"what is the appropriate size for a clinical trail--when have we tested enough?" and "how can decision-makers prioritize new health interventions?" The second question in particular is very complex and situation-dependent. Many people are wrestling with it these days.

For readers interested in HPV and cervical cancer per se, there is a lot of interesting material at RHO Cervical Cancer (www.rho.org), especially in the Cervical Cancer Library. That site does not receive any industry funding.